Remove the last erroneous command.

[vegansk]

For example, here is the log:

> let x = 123
> x
nrpltmp.nim(2, 1) Error: value of type 'int' has to be discarded

This PR removes x line from the history.

And also it compiles again :-) (checked on the latest devel).

[vegansk]

Also removed this error on Ctrl+D:

> Traceback (most recent call last)
nrpl.nim(89)             nrpl
sysio.nim(140)           readLine
sysio.nim(51)            raiseEIO
system.nim(2530)         sysFatal
Error: unhandled exception: EOF reached [IOError]